Answer: Methylmercury is lipophilic, bioaccumulates in organism tissues, and biomagnifies up food chains; humans consuming top-predator fish can receive doses causing irreversible neurological damage (Minamata disease).
- A Methylmercury is water-soluble and rapidly excreted by fish, so it disperses quickly through large volumes of water without accumulating in the majority of documented cases as widely reported in standard reference material
- B Methylmercury is lipophilic, bioaccumulates in organism tissues, and biomagnifies up food chains; humans consuming top-predator fish can receive doses causing irreversible neurological damage (Minamata disease)
- C The conversion is mainly significant in oceans; freshwater lakes and bays are unaffected because brackish conditions inhibit the methylating bacteria under most conditions studied in most observed cases under typical physiological conditions
- D Methylmercury binds to carbonate ions in water, neutralising its toxicity by forming an insoluble precipitate according to standard texts in general clinical practice as frequently documented in most reference accounts
Correct answer: B. Methylmercury is lipophilic, bioaccumulates in organism tissues, and biomagnifies up food chains; humans consuming top-predator fish can receive doses causing irreversible neurological damage (Minamata disease)
Explanation: Methylmercury (CH₃Hg⁺), produced by methylcobalamin-dependent anaerobic bacteria in sediments, is far more dangerous than Hg²⁺ because it is lipophilic - it crosses biological membranes efficiently, is poorly excreted, and binds strongly to thiol groups in proteins. It biomagnifies dramatically up food chains (plankton → small fish → large fish → humans), and even small human doses cause permanent neurological damage, sensory loss, paralysis, and congenital defects, as seen in the 1950s Minamata Bay tragedy.
Classical smog is a reducing mixture of SO₂ and fog, while photochemical smog is an oxidising mixture generated by UV-driven reactions of NOx and hydrocarbons.
Concept context
Understand how human activities alter the atmosphere, water, and soil. Covers air pollutants, smog types, ozone depletion, acid rain, greenhouse effect, water and soil pollution, and the principles of green chemistry.